Apparatus for treating granular products by drying, film-coating or coating are known in a variety of forms. For a representative sample, reference is made to the following publications:
EP 0 080 199 A2
EP 0 732 882 B1
WO 01/26601
The publication EP 0 080 199 A2 discloses an apparatus for treating granular products by drying, film-coating or coating. It comprises a drum mounted so as to rotate about a horizontal axis, in which inlet and outlet lines for a gas for drying a product contained in the drum are connected to an immersion member that has inlet and outlet openings for the gas and within the drum assumes a position in which it is immersed in the product. The immersion member is in the form of a tunnel through which the product can flow, inside which are provided at least some of the inlet and outlet openings for the gas. The tunnel is aligned in the direction of flow of the product, in the position of installation. If there is product in the drum, moistening medium emerging from a nozzle, for example, is sprayed onto the product from above and below while the drum rotates. The upper layer of product flows downwards at an angle to the horizontal. The immersion member is immersed in this downward flowing layer of product. The immersion member comprises an intermediate base which in cooperation with axial partition walls and partition walls provided in the direction of flow divides it into an annular inlet chamber for drying gas and a flat outlet chamber. The inlet chamber is connected to an inlet line and the outlet chamber is connected to an outline line. The intermediate base has slot-shaped inlet openings that extend over the entire width and open up a path for the drying gas from the inlet chamber into the inner space of the tunnel formed by the immersion member. In this solution the amount of product subjected to direct drying is dependent on the geometry of the tunnel, the depth of immersion and the arrangement of the outlet channels and therefore has to be specifically adapted to each individual case. Moreover, for optimum drying, it is necessary to ensure on the one hand an internal width of the inlet cross section depending on the width of the drum and furthermore a specific predefined level of filling of the drum, which in the position of installation of the immersion member always guarantees that it is filled between the intermediate base and intermediate ceiling. The product is dried from below, which can lead to unsatisfactory and uneven drying results if the fill level is high and there is a correspondingly great tunnel height. Admittedly, the slot-like design of the outlet openings for the drying gas ensure direct drying over a fairly large area in the direction of flow, but the entire annular chamber is supplied through only a single inlet chamber. A further disadvantage is the complex geometry of the element that forms the tunnel and carries the outlet openings for the drying gas, which requires specific adaptation to the design of the drum, the lack of exchangeability and lack of adaptability to changing fill levels.
From the publication EP 0 732 882 B1 a design of an apparatus for treating granular products is known which makes it possible to dry granular products in a rotatably mounted coating pan through air outlet means provided with perforated hollow bodies that can be immersed in the product. The outlet openings are arranged on tubular elements that extend radially from a distribution channel and are thus in a fixed position relative to the distribution channel. Depending on the fill level of the drum, different depths of immersion of the air outlet means in the product are provided, that are reflected in different drying results. In addition, because of the radially aligned arrangement of the outlet openings and their cross-sections, the activity and hence drying areas extend only in an annular configuration around them.
To solve the problem, telescope-like hollow bodies are known from WO 01/26601, which are adjustable in length, extend vertically from the distribution channel and can be immersed in the moving mass of the product that is to be treated. In their distal part the hollow bodies have an elongate cross section with pointed ends, that is open at the bottom, forming the outlet openings, and also has perforated areas on the side walls for the exit of the drying gas. The effective drying area can thus be enlarged. However, a disadvantage here is the greatly limited drying area around the outlet openings on the telescopic hollow bodies, extending around the individual hollow bodies, the drying action decreasing in the radial direction.